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What are Populations and Communities?

What are Populations and Communities?

Microbial Interactions: Competition

Microbial Interactions: Competition

Microbial competition is an ecological interaction in which microorganisms vie for limited resources within shared environments. These resources may include nutrients, space, or light, depending on the system. The intensity and outcome of competition are influenced by the environmental context, such as nutrient availability, spatial constraints, and the diversity of microbial species present. These competitive interactions significantly influence the structure, function, and resilience of...

Competition

Competition

When organisms require the same limited resources within an environment, they may have to compete for them. Competition is a net-negative interaction. Even if two competing individuals or populations do not interact directly, the overall fitness of both competitors is lowered as a result of not having full access to the limited resource.

Population Growth

Population Growth

Population size is dynamic, increasing with birth rates and immigration, and decreasing with death rates and emigration. In ideal conditions with unlimited resources, populations can increase exponentially, which plots as a J-shaped growth rate curve of population size against time. This type of curve is characteristic of newly-introduced invasive species, or populations that have suffered catastrophic declines and are rebounding.

Frequency-dependent Selection

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.

Conservation of Small Populations

Conservation of Small Populations

Small population sizes put a species at extreme risk of extinction due to a lack of variation, and a consequent decrease in adaptability. This weakens the chances of survival under pressures such as climate change, competition from other species, or new diseases. Large populations are more likely to survive pressures such as these, as such populations are more likely to harbor individuals that have genetic variants that are adaptive under new stresses. Small populations are much less likely to...

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Related Experiment Video

Updated: May 17, 2026

Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems

Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems

Published on: July 30, 2019

Size-dependent mortality and competition interactively shape community diversity.

Barbara Taborsky¹, Mikko Heino, Ulf Dieckmann

¹Behavioural Ecology, Institute of Ecology and Evolution, University of Bern, Wohlenstrasse 50A, CH-3032 Hinterkappelen, Switzerland. barbara.taborsky@iee.unibe.ch

Evolution; International Journal of Organic Evolution

|October 31, 2012

Summary

This summary is machine-generated.

Body size evolution is shaped by competition and mortality. This study reveals how their interaction can create diverse body size morphs, influencing community structure and biodiversity patterns.

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Area of Science:

Ecology
Evolutionary Biology
Theoretical Biology

Background:

Body size is a key factor in evolutionary processes like sympatric diversification and community structuring.
Distinct body size morphs can arise from size-dependent competition and size-dependent mortality.

Purpose of the Study:

To investigate the interactive effects of size-dependent competition and mortality on body-size evolution.
To determine if these interactive forces can lead to the emergence of multiple, coexisting size morphs.

Main Methods:

Developed a theoretical model allowing size-dependent competition and mortality to interact.
Analyzed the model's outcomes on body-size evolution and community structure.

Main Results:

Size-dependent mortality, in conjunction with size-dependent competition, can generate multiple coexisting size morphs.
Interactions between these forces cause abrupt shifts in size structure and non-monotonic biodiversity patterns along environmental gradients.
Size-dependent competition favors small, similar body-size ratios, while size-dependent mortality allows for greater size disparity.

Conclusions:

The interplay between size-dependent competition and mortality is crucial for understanding body-size evolution and diversification.
Distinct patterns in body-size ratios across communities can serve as indicators for the concurrent action and relative importance of these selective forces in nature.